Vapor compression refrigeration systems conventionally employ a condenser which receives a refrigerant in the vapor phase under relatively high pressure from a compressor. The condenser is operative to condense the refrigerant vapor to the liquid phase for ultimate transmittal to an evaporator whereat the refrigerant evaporates. Heat from the ambient is rejected to the refrigerant where it is absorbed as the latent heat of vaporization as the refrigerant evaporates. The now vaporized refrigerant is then directed to the compressor to be recycled through the system.
Conventionally such systems include a so-called receiver which is intended to receive liquid refrigerant from the condenser before it is transmitted to the evaporator. The primary purpose of the receiver is to assure that all refrigerant passed to an expansion device upstream of the evaporator is in the liquid phase. This means that the refrigerant quality is low and its enthalpy is also low to increase the evaporator's ability to absorb heat as the refrigerant evaporates. In this connection, the receiver acts as a reservoir for excess liquid refrigerant to assure that only liquid is fed to the expansion device in spite of system changes typically caused by the operation of the compressor. For example, in an automotive air conditioning system, the compressor is frequently stopped and started. Furthermore, when the engine to which the compressor is typically mechanically coupled is accelerating, compressor speed may also change, causing a change in the pressure at its inlet which in turn affects the flow rate of refrigerant in the system.
In addition, receivers may also be provided with a means for filtering the refrigerant as well as for drying the refrigerant to assure its purity, thereby avoiding inefficient operation.
It is desirable to integrate the receiver with the condenser in many instances. For example, in so-called parallel flow condensers of the multipass type, integration of the receiver with the condenser assures that only liquid refrigerant will be fed to the last pass of the condenser which then acts solely as a subcooling pass. When such is accomplished, the increased subcooling further lowers the refrigerant quality while reducing the enthalpy of the refrigerant delivered to the evaporator to achieve the efficiencies mentioned earlier. Moreover, integration of the receiver with the condenser eliminates the need for a separate receiver/dryer elsewhere in the system and has the ability to reduce the total cost of the system as well as the quantity of refrigerant that must be charged into the system.
In this latter respect, it is well known that certain refrigerants are not environmentally friendly. For example, CFC 12 is thought to degrade the protection ozone layer surrounding the earth. Other refrigerants such as HFC 134a, while less damaging of the ozone layer, are thought to contribute to the so-called greenhouse effect which may be responsible for global warming.
Because in automotive air conditioning systems, the compressor is driven by the vehicle engine, it cannot be hermetically sealed as in residential or commercial air conditioning units. As a consequence, there is the potential for escape of the refrigerant through compressor seals with the resulting deleterious effects on the environment. Thus, refrigerant charge volume is of substantial concern.
In U.S. Pat. No. 5,546,761 issued Aug. 20, 1996 to Matsuo et al, there is disclosed an integrated receiver/condenser. One difficulty with the type of system disclosed in that patent is that turbulence may be induced within the receiver. The turbulence may be induced by the incoming refrigerant which typically will be a mixture of vapor and liquid phase refrigerant. Another source of turbulence, particularly when the receiver/condenser is employed in a vehicular air conditioning system, is vehicular speed changes. As the vehicle accelerates or decelerates, liquid refrigerant within the receiver may undergo substantial shifts in its position in relation to the receiver outlet.
When such turbulence is present, it is possible for refrigerant as a mixture of liquid and vapor to reach the receiver outlet. When that occurs, the last pass of the condenser is no longer exclusively a subcooling pass. Rather, it will not only act to subcool that refrigerant that is in the liquid phase, but it will act to condense that refrigerant which is in the vapor phase. As a consequence, the optimal degree of subcooling cannot be achieved and system operation suffers.
The present invention is directed to overcoming one or more of the above problems.